Ariel Castro (center), 53, hanged himself in prison shortly after he was sentenced to life in prison, plus 1,000 years.

The Cleveland monster who tortured and abused three women he held captive for more than a decade became willing to let his victims go free, but was too coward to surrender to authorities, his lawyer said.

Ariel Castro allegedly told one of his victims, Amanda Berry — who mothered the brute’s daughter during her captivity — that the end was near and began leaving doors unlocked before she managed to escape on May 6, 2013.

After she slipped out of the Seymour Ave. home, authorities came and rescued Castro’s two other victims, Michelle Knight and Gina DeJesus.

From left: Amanda Berry, Gina DeJesus and Michelle Knight soon after they were rescued from Castro’s house of horrors in May 2013.

(HENNES PAYNTER COMMUNICATIONS/HANDOUT/EPA)

“He intentionally became much more negligent in the house about locking the door and keeping them inside,” the lawyer, Craig Weintraub, told WKYC-TV.

“He didn’t have the courage to go to the police department and surrender, and the only way this was going to happen is if he was negligent and allowed them to leave the house and be able to find a way out while he was gone a few hours.”

Craig Weintraub was one of the two attorneys representing Ariel Castro after he was arrested on a battery of kidnapping and rape charges.

(WKYC)

Weintraub said Castro — who hanged himself in prison soon after he was sentenced — began to change as Berry’s daughter grew older.

“It wasn’t going well any longer,” Weintraub told the local NBC affiliate. “His daughter was at an age that she should not be in the house anymore. She needed to be in school and be in a normal environment.”

Amanda Berry (right) hugs her sister, Beth Serrano, after being reunited in a Cleveland hospital.

(AP)

Castro had tried to create a sense of family with his victims and even recorded videos — all of which are being held by the FBI — that show them celebrating holidays.

“What was startling to me was watching the videos of the Easter celebrations in the house, searching for Easter eggs, hunting for Easter eggs,” said Weintraub, who saw the clips.

“As well as the Christmas celebration, like it was a normal family.”

Weintraub said Castro, 53, who prefered to sit naked in his jail cell during their interviews, told him that he even joked with his victims about the money they could make by writing books about the horrifying ordeal.

Knight — who changed her name to Lillian Rose Lee — wrote a memoir, “Finding Me,” which was published this week.